Wind Turbine Design and Feasibility Report 2

8/9/2019 Wind Turbine Design and Feasibility Report 2

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DESIGN OF A WIND TURBINE

Abstract

The project in hand deals with the designing, feasibility and cost

effectiveness study of a wind turbine which may preferably be installed at

agricultural farms and open areas where there are no major hindrances to

the wind current or tower height limitations. This type of wind turbine

system is used to fulfill the local electricity power requirements of the site.

The project is done by three students and each students report emphasizes

on a particular area in addition to the overall design brief. In this report, the

detailed discussion on types of wind turbines as well as the detailed design

of turbine blade is discussed.

PLANNING AND ORGANIZING YOUR PROJECT

The goal of the project is to come up with an optimum design of wind

turbine which is suitable for the power requirements of an average

agricultural form in USA in particular and worldwide in general. Following

breakdown was selected to achieve the objectives:

(a) Selection of wind turbine type(b) Selecting Vital parameters of the system based on requirement and

cost comparison

(c) Finalizing the details of(i) Blade design(ii) Gearbox design(iii) Yaw and steering system(iv) Transmission system(v) Number of blades(vi) Generator(vii) Tower(viii) Hydraulic System(ix) Brake System

(d) Making performance and cost comparison


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(e) Incorporating safeties in design(f) Estimating the cost of project

THE ITERATIVE NATURE OF DESIGN

Selection of Type of Wind Turbine

There are two basic types of turbines: -

Drag Type Turbines These are the types of turbine which are sent into

motion due to the drag effect of the media (either air or water). Figure No 1

and 2 shows some basic shapes and arrangements for drag type turbines.

These turbines were mostly used in the early history in Persia and China.

These may be classified as:

(i) Persian Windmill(ii) Chinese Windmill(iii) Saviounus

Figure No 1 Different types of Drag Type Wind Turbines


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(b) Lift Type Turbines These types of turbines have airfoil typegeometry of blades and use the concept of lift generation to extract

energy from air. These wind turbines are most common now a

days. Followings are the subcategories of these turbines.

(i) Horizontal Axis Wind Turbine (HAWT) This is themost common type of wind turbine. These have their main rotor

shaft and electrical generator at the top of a tower. These rotor

must be pointed into the wind.

(ii) Vertical Axis Wind Turbine (VAWT) In this type, themain rotor shaft is installed vertically. The blades need not be

steered to keep in wind direction.

Figure No 2 Different Arrangements in Drag Type Wind Turbines

HAWTs

Disadvantage The greatest design complexity faced in case of

Horizontal axis wind turbines (HAWT) is that these must be pointed into the

wind in order to work efficiently. For steering small turbines, a simple wind

vane is used, while large turbines generally use a wind sensor coupled with a

servo motor.


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Advantages This type of turbines has following advantages due to

which it suites our requirements: -

(a) The blade pitch angle can be varied to give the turbine blades anoptimum angle of attack. This feature enables the turbine to

collects the maximum amount of wind energy for any time of the

day and during any season.

(b) The tall tower base allows access to stronger wind in sites with windshear. In some wind shear sites, every ten meters up, the wind

speed can increase by 20% and the power output by 34%.

(c) Since the blades always move perpendicular to the wind, theyreceive power through the whole rotation and hence are more

efficient. In contrast, all vertical axis wind turbines involve varioustypes of reciprocating actions, requiring airfoil surfaces to backtrack

against the wind for part of the cycle. Backtracking against the wind

leads to inherently lower efficiency.

(d) The face of a horizontal axis blade is struck by the wind at aconsistent angle regardless of the position in its rotation. These

results in a consistent lateral wind loading over the course of a

rotation, reducing vibration and audible noise coupled to the tower

or mount.

Figure No 3 Typical Horizontal Axis Wind Turbines


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VAWTs

It is difficult to mount vertical-axis turbines on towers. These are often

installed nearer to the base on which they rest, such as the ground or a

building rooftop. This attribute of VAWTs make them more suitable for

installation in populated areas, inside the cities (mounted on building

rooftops) or at places where there is a restriction on maximum height of the

building structures. Moreover, due to less height of the blades, they do not

get sufficient wind speed and hence are not as effective (in general) as

HAWTs.

Figure No 4 Typical Vertical Axis Wind Turbines

Keeping in view the above discussion, Horizontal Axis Wind Turbine

(HAWT) was selected as most suitable option for type of wind turbine to be

installed on farm lands.


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Figure No 5 Different Arrangements in Lift Type Wind Turbines

IDEAS GENERATION

Optimum Locations for Installation

The installed location of wind turbine is one of the most important factors

dictating the design of the system. As mentioned in the basic design

requirements, the current system is being designed for large agricultural

farms. So, followings design features may readily be concluded as these are

the most feasible options for intended installation locations: -

(a) Horizontal Axis Wind Turbine may be installed without any majorlimitations of tower height or area requirements.

(b) Power requirements generally remain uniform throughout the year(c) Wind changes its speed and direction smoothly. So the turbine may

not experience frequent variation of wind speed or directions. The

chances of wind gusting are also less frequent.


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(d) As most of the farms are generally far off from cities where majormaintenance facilities are established; the design should call for

minimum maintenance requirement and a reliable operation.

Wind Power Density

Wind Power Density or WPD is defined as the effective force of the

wind at a particular location. It is a yardstick which frequently used to

determine good locations for installation of wind turbines. Mathematically,

wind power may be expressed as:

1

2

1

2

1

2

1

2

1

2

Figure No 6. A Typical Wind Speed Distribution Chart


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The above relation shows that the wind power increases with the cube

of the wind velocity. So, wind speed is the most influential variable defining

the wind power density. Figure 6 shows a typical wind speed distribution

chart for a typical location. This chart provides the most important data for

installation of wind turbine.

However, it is not possible to capture 100% of the wind power.

Generally, the most efficient systems have efficiency not more than 55 to

60%.

Rated Power of the System

The system to be designed is required to have a rated output from 800

KW to 1000 KW. This is the power output which can fulfill the requirements

of most of the agricultural farms worldwide thus enhancing the chances of

acceptability for the users all over the world. The wind turbines of this

capacity fall under the category ofMedium Sized Turbine Systems.

Finalization of Basic Design Features

Base on the discussion made above, the basic design features for the

Wind Turbine are estimated. The design process will be started based on this

design feature and further refinement will be carried out subsequently.

Wind Turbine Type Horizontal Axis Wind Turbine

Rated Power Range 800-1000 KWRotor Diameter 40 60 m

Hub Height 60 80 m

Sweep Area 1800 m2

Number of Blades 3

Brake System Yes

Yaw Control Yes (Preferably an active control system)

NEGOTIATION OF A DESIGN BRIEF

Blade design

Blades can be made from simple objects as barrels. New generation

wind turbine designs are pushing power generation from the single

megawatt range to upwards of 10 megawatts. The common trend of these


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larger capacity designs are larger and larger turbine blades. Thus they cover

a larger area and effectively increase the tip speed ratio of turbine at a given

wind speed. In this way, the energy extraction capability may be enhanced

many times. A blade size of 25 meter was selected to fulfill the design

requirements.

Tip Speed Ratio

The ratio between the speed of the wind and the speed the blade tips

is called Tip speed ratio. High efficiency 3-blade-turbines have tip

speed/wind speed ratios of 6 to 7.

Figure No 7 Blades of Wind Turbine


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Blade materials

Following options were considered to finalize the material for blade

manufacturing.

Option-1 Aluminum, Wood or Canvas Smaller blades can bemade from light metals such as aluminum. Wood and canvas sails were

originally used on early windmills due to their low price, availability, and

ease of manufacture. These materials, however, require frequent

maintenance during their lifetime. Also, wood and canvas have a relatively

high drag (low aerodynamic efficiency) as compared to the force they

capture. For these reasons these materials are not opted for current design.

Option-2 Composite Material Option Use of fiber reinforcedcomposites is increasing in wind turbine industry. In 2001, an estimated 50

million kilograms of fiberglass laminate were used in wind turbine blades.

New materials and manufacturing methods provide the opportunity to

improve wind turbine efficiency by allowing for larger, stronger blades.

In case of composites there are three main types which may used in

blade manufacturing. These are:

(a) Preimpregnated Composites(b) Epoxy based Composites(c) Carbon Fiber Reinforced Composites

Figure No 8 A Typical Wind Turbine Blade


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Preimpregnated Composites Preimpregnated composites are an

option for blade design. However, they come with following limitation:

(a) Production of thick laminates necessary for structural componentsbecomes difficult.

(b) Bleeding is required to eliminate voids and insure proper resindistribution.

(c) Manual fabrication process lacks standardization.Epoxy based Composites Epoxy-based composites are of greatest

interest to wind turbine manufacturers because they deliver a key

combination of environmental, production, and cost advantages over other

resin systems. Epoxies also improve wind turbine blade composite

manufacturing due to the followings:

(a) Shorter cure cycles(b) Enhanced durability(c) Improved surface finish.

Carbon Fiber Reinforced Composites Carbon fiber-reinforced load-

bearing spars have recently been identified as a cost-effective means for

reducing weight and increasing stiffness. However, they have the inherent

limitations of fabrications difficulty and relatively high cost of material.

Keeping in view the above discussion, Epoxy Based Glass Reinforced

composite material was used as the material for blade. Moreover, an

integrated wire meshing was provided inside the composite layer which

provides lightening protection besides giving an extra strength to the blade.

COSTING OF PRODUCTS

Cost of the system was estimated to be $ 0.25 million for each unit.

The cost contains material and labor cost of all the individual components

and systems. The detailed cost calculations are done by the other students

report.


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BALANCING DESIGN/PERFORMANCE NEEDS

Following is the summary of other design features incorporated in the

system based on the operational requirements. A detailed discussion is

made in the other students report.

Operating Temp Range -2 to 40 degree C

Turbine Diameter 50 m

Tower Height 80 m

Twisted rotor Blade Yes

Blade Count 3

Power Control Active

Speed Control System Yes

Brake System Hydraulic Brake with redundancy

Sweep Area 1800 m2

Rated Power Output 1 MWYaw Control Passive

DESIGN FOR SAFETY

The design of wind turbine is incorporated with various safeties. The brake

system is made redundant to prevent the turbine from moving freely in case

of brake failure. Moreover, the factor of safety in blade strength is kept on

higher side to avoid blade failure. A wire mesh in blade material provides

extra strength to the blade as well as provides lightening protection. Aircraft

anti-collision arrangements have been made. In addition to this active speed

control systems and pitch control systems are incorporated to avoid blade

stall or over speeding which may cause rupturing of blades.


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LITERATURE SEARCH

1. A Wind Energy Pioneer: Charles F. Brush, Danish Wind IndustryAssociation

2. http://www.windpower.org/en/pictures/brush.htm3. "Part 1 Early History Through 1875".4. http://www.telosnet.com/wind/early.html.5. A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961), pp. 145-

151

6. Dietrich Lohrmann, "Von der stlichen zur westlichen Windmhle",Archiv fr Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1-30 (10f.)

7. Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology:An illustrated history, p. 54. Cambridge University Press. ISBN 0-521-

42239-6.

8. Donald Routledge Hill, "Mechanical Engineering in the Medieval NearEast", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge

Hill, Mechanical Engineering)

9. "James Blyth". Oxford Dictionary of National Biography. OxfordUniversity Press.

10. http://www.oxforddnb.com/public/dnb/100957.html.11. a b Quirky old-style contraptions make water from wind on the

mesas of West Texas.

12. Alan Wyatt: Electric Power: Challenges and Choices. Book PressLtd., Toronto 1986, ISBN 0-920650-00-7

13. Kansas Wind Energy Project, Affiliated Atlantic & Western GroupInc, 5250 W 94th Terrace, Prairie Village, Kansas 66207

14. "Wind Energy Basics". American Wind Energy Association.15. http://www.awea.org/faq/wwt_basics.html.

Wind Turbine Design and Feasibility Report 2

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